152 



tricose in the anterior half; beaks closely incurved; a sharp umbonial 

 ridge running from the beak nearly to the posterior extremity ; from this 

 ridge the surface descends with a concave slope to the hinge-line and 

 dorsal margin ; hinge-line straight, with a well-developed concave area. 

 The anterior extremity is small and rounded ; the ventral margin strongly 

 convex in the anterior half and somewhat straight behind. 



Of this fine new species I have seen only the one figured. 



Dedicated to the discoverer, Prof. H. Y. Hind, of Trinity College, 

 Toronto. 



Locality and Formation. — Near Toronto ; Hudson River group. 



Collector.— Pvoi. H. Y. Hind. 



Ctbnodonta Iphigbnia. (N. sp.) 



Fig. 132. 

 Fig. 132. — Ctenodonta Iphigenia. Right valve. 



Description. — Transversely sub-ovate ; umbones a little behind the 

 mid-length ; anterior extremity large and broadly rounded ; from the um- 

 bones the sheU tapers to a narrow, rounded posterior extremity which 

 occupies the lower one third next the ventral margin. The greatest con- 

 vexity is a little in front of the middle. A portion of the ventral margin 

 ia the posterior two thirds of the length is gently concave. The umbones 

 are somewhat flattened by a wide shallow byssal sinus which descends to 

 the ventral margin. There is a somewhat sharply angular umbonial ridge 

 running from the beaks to the posterior extremity. Between this ridge 

 and the hinge-line there is an elongated imperfect lunette. The beaks 

 appear to be closely incurved. Surface unknown. 



Transverse length about 1 inch; distance from the umbones to the 

 ventral margin half an inch. 



Of this species we have only a single specimen, — a right valve. It 

 resembles 0. nasuta, but differs from that species by having a strong pos- 

 terior umbonial ridge. 



Locality and Formation. — Cape Smith, Lake Huron; Hudson River 

 formation. 



Oollector.—R. Bell. 



